1. Field of the Invention
This invention relates generally to the field of auxiliary equipment for marine seismic cables and more particularly to the attachment of equipment to cables, and even more particularly to the shape and construction of the connector.
2. Description of the Prior Art
In the course of conducting marine seismic surveys for oil and gas, it is customary to tow cables, often 3 to 10 kilometers in length, beneath the surface and astern of a survey ship. As many as twelve of these cables are towed at one time. Each cable contains multiple hydrophones as well as associated electronics and other sensors required in the data acquisition process. The cables are called xe2x80x9cstreamersxe2x80x9d and are constructed using semi-solid plastic material or oil filled flexible tubing. They are typically two to three inches in diameter.
When conducting seismic surveys, the depth of the cable must be maintained at a precise distance from the surface. This is accomplished by the use of depth control devices that are attached to the exterior of the streamer cable using collars which are secured around the cable and result in a bearing comprising an inner race and an outer race that allows the cable to be free to rotate within the attachment point. The outer race and inner race are constructed and assembled so that they can rotate with respect to each other. The outer race is attached to the depth control device. Other types of modules for other purposes are attached in the same manner.
As the cable is towed through the water, it is very important that self-generated noise be minimized, because the noise interferes with reception of the signals of interest. Any abrupt physical upset of the cylindrical shape of the cable produces turbulence, thereby creating unwanted noise. Also there is need to avoid damage to the streamer cable where the outer race remains on the cable during streamer windup on a reel.
Common practice and prior art is described in a number of patents such as:
U.S. Pat. No. 4,290,124 Cole, Jimmy R. Remote Control Cable Depth Control Apparatus
U.S. Pat. No. 4,709,355 Woods et al Controller for Marine Seismic Activity
U.S. Pat. No. 5,529,011 Williams, Oneil J. Connector for Underwater Cables
A primary object of this invention is to provide an outer race for a collar that reduces self-generated noise when being towed through the water.
Another object of the invention is to construct an outer race which when left connected to a streamer cable and wound on a rotating storage reel, does minimal damage to the streamer cable beneath.
The objects identified above and other features and advantages of the invention are incorporated by providing an outer race that minimizes noise generation and prevents damage to the cable and to itself when pulled onto a survey vessel and wound on a reel. The outer race is a split and hinged device that can be placed around the inner race and latched in place. The outer race is constructed of two different types of plastic material. The central portion of the race is made of a strong rigid plastic material. The frustro-conical fairings that extend from each end of the outer race serve as fairings to minimize turbulence when the streamer is pulled through the water. The fairings are constructed of compliant plastic material. The soft fairings can be wound around a reel while under tension to inhibit damage to the inner race or to the cable itself.